Power supply



Nov. 27, 1956 B. E. DENTON 2,772,371

POWER SUPPLY Filed Jan. 3, 1956 IN V EN TOR.

ATTOBNEJ.

United States Patent POWER SUPPLY Bethel E. Danton, Haddonfield, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application January 3, 1956, Serial No. 557,077 9 Claims. (Cl. 307-150) This invention relates to power supplies, and more particularly to power supplies of the transformerless fullwave doubler type adapted to provide operating voltages for a radio or television receiver. Power supplies embodying the present invention are particularly applicable to provide operating voltages for electronic apparatus wherein a plurality of electron tube heaters or tube filaments are connected in series.

It has been proposed to energize a series-connected heater string or series-connected filament string from many types of radio receiver power supplies by connecting the series-connected string directly across the alternating current (A.-C.) input terminals to the power supply. Where the power supply is of the transformerless full-wave doubler type, however, a string of heaters, for example, cannot be connected directly across the A.-C. input terminals because the voltage of some of the heaters will oscillate between a minimum value, near the chassis ground, and the maximum value equal to approximately twice the peak of the input A.-C. voltage. Many of the tubes designed for series heater operation are not rated to withstand this potential difference between their heaters and their cathodes. Hence, direct connections of a series-connected heater string across the A.-C. input terminals to a full-wave doubler power supply are not practical. It has been necessary, in many cases heretofore, to employ a transformer for supplying the proper heater voltage for such a series-connected heater string.

Accordingly, it is an object of the present invention to provide an improved power supply of the transformerless full-wave doubler type adapted to provide an operating voltage for a plurality of heaters connected in series.

It is another object of the present invention to provide an improved transformerless full-wave voltage doubler power supply, for electronic equipment employing electron tubes having heaters connected in series with each other, that will overcome the aforementioned disadvantages.

It is still another object of the present invention to provide a power supply of the transformerless full-wave doubler type for providing an operating voltage to a series-connected heater string in a manner whereby the peak voltage of the energizing alternating current applied to the power supply is the greatest possible voltage applied across the series-connected heater string.

A further object of the present invention is to provide an improved power supply of the transformerless fullwave doubler type, adapted to energize a series-connected heater string safely, that is simple in construction and operation, easy and economical to manufacture, and yet highly efiicient in use.

In accordance with the present invention, the foregoing objects and related advantages are attained in an improved transformerless full-wave voltage doubler power supply wherein operating voltages for a series-connected heater string is obtained by connecting each end of the heater string through a separate capacitor to each of the A.-C. input terminals to the power supply, and connecting one end of the heater string to the negative output terminal of the B voltage supply for referencing the heater voltages thereabout. Means are also provided to cancel voltage ripple in the B voltage rectified output by means of a voltage of equal and opposite phase derived from the A.-C. voltage input to the power supply.

The novel features of the present invention, as well as the invention itself, will be understood in detail from the following description when considered in connection with the accompanying drawing, in which similar reference characters represent similar parts, and in which:

Fig. l is a schematic diagram of a transformerless fullwave doubler power supply in accordance with the present invention;

Fig. 2 is a schematic diagram of a modification of the transformerless full-wave doubler power supply in accordance with the present invention; and

Fig. 3 is still another modification of a transformerless full-wave voltage doubler supply of the present invention.

Referring now particularly to Fig. 1, there is shown a transformerless full-wave voltage doubler power supply 10 of the type adapted to provide an operating voltage for a series-connected heater string 12 of heaters A, B, C L, M, N. The heater string 12 is shown, in part, as a broken line to indicate that it may contain a plurality of heaters, although only six are illustrated. In some television receivers, the heater string 12 may comprise as many as twenty heaters.

The power supply 10 has a pair of input terminals 14 and 16 adapted to be connected to any suitable source of A.-C. voltage, say 117 A.-C. volts. The input terminal 14 is connected to the anode of a diode 18, of a voltage doubler circuit 20, through a switch 22 and a resistor 24. The diode 18 may be of the selenium or germanium type, as well as of the electron discharge type. The resistor 24 may have a negative temperature coefficient. A resistor 24, for example, having a cold resistance of 13 ohms and a hot resistance of 0.4 ohm, has been found satisfactory. Such a resistor 24 will prevent excessive current flow through the diode 18 when the switch 22 is first closed. A diode 26, similar to the diode 18, is connected in series with the diode 18 and with the resistor 24. A pair of serially connected capacitors 28 and 30 are connected in series with the cathode of the diode 18 and with the anode of the diode 26. The input terminal 16 is connected to the common junction of the serially connected capacitors 28 and 30. The diodes 18 and 26 and the capacitors 28 and 30 comprise the voltage doubler circuit 20 wherein the direct current (D.-C.) voltage across each of the capacitors 28 and 30 is approximately equal to the amplitude of the peak A.-C. voltage applied between the input terminals 14 and 16.

The output of the voltage doubler circuit 20 is filtered by a filter 31 comprising a choke 32 and a capacitor 34. The choke 32 is connected between the cathode of the diode 18 and 13+ voltage output terminal 36. The eapacitor 34 is connected across the output terminal 36 and the anode of the diode 26. A load 38, represented herein as a resistor 38, is connected between the B+ output terminal 36 and a negative (B) output terminal 40. The negative output terminal 40 is connected to the anode of the diode 26 and also to a common connection, which may be the chassis of the power supply 10, and represented herein by the ground symbol.

It will now be understood that when the switch 22 is closed an alternating voltage applied between the input terminals 14 and 16 is rectified and doubled by the voltage doubler circuit 20 and applied, as a filtered D.-C. B supply voltage, across the load 38.

Means are provided to connect the series-connected heater string 12 across the input terminals 14 and 16 in a manner whereby more of the tubes (not shown) will have a voltage applied between their heaters and cathodes (not shown) greater than the peak voltage applied across the input terminals 14 and 16. To this end, a heater output terminal 42 is connected tothe output terminal. ltd-through a capacitor 44, a voltage dropping resistor 45,,and the switch 22. Another heater output terminal% is connected to the input terminal 16 through a capacitor 48. One end of the heater string, that is the heater A,- is. connected to the heater output terminal 42, andthe other end of the heater string 12, that is theheater N, is connected to the heater output terminal 46.. Under these conditions, the A.-C. voltage across the heater string 12 can never exceed the A.-C. voltage appliedbetween the inputv terminals 14 and 16, andthe D.-C. component of the full-Wave doubler circuit 20 is isolated from the heater string 12. By connecting the heater output terminal 46 to the negative (B) output terminal 40, through a resistor d, the heater string 12 is referenced to the potential of the chassis ground. It will be understood that if the heater string 12 were connected directly across the A.-C. input terminals 14 and 16, that is, if the capacitors 44 and 48 were shorted, the peak voltage at the heater A with respect to ground would be approximately twice the peak input voltage applied between the input terminals 14 and 16. The reasontfor this is the common junction of the capacitors 2S and 30 is at a D.-C. voltage approximately equal to the peak line voltage with respect to the chassis ground, and the maximum voltage at the heater A with respect to ground will approach twice the peak input voltage. Since the cathodes (not shown) of the tubes (not shown) heated by the heaters A N are usually maintained at or near ground potential, the heater-tocathode voltage in some tubes would be substantially twice the peak line voltage if the heater string 12 were connected directly across the input line voltage. In most cases this heater-to-cathode voltage is greater than the rated heater-to-cathode voltage for the tubes. By capacitively coupling the heater string 12 at both ends to the line voltage,,the heater-to-cathode voltage is never greater than the peak line voltage, and is maintained at a safe operating voltage.

Referring now to Fig. 2, there is shown a modification 60' of the transformerless full-wave voltage doubler power supply of the present invention wherein the capacitor 30 of the voltage doubler circuit 26 is used to connect: the heater output terminal 46 to the input terminal-16. The heater output terminal 46 is connected to the capacitor 30 through a resistor 62 of relatively low impedance. In the modification 60 of the power supply, the choke 32 of the filter 31, is connected between the. anode of the diode 26 and the negative output terminal 40 of the B supply. Since the capacitor 3t; will now have the A.-C. current that flows through the heater string 12. flow through it, a 60 cycle ripple will be produced at the output terminal 36. This ripple can be cancelled by a bucking voltage whose amplitude and phase are determined by the resistor 50 and a capacitor 64. The capacitor 64 is connected between the heater output terminal 42 and the chassis ground. Thus, a component of the heater current, of proper pulse and amplitude, will flow through the resistor 50 and the capacitor 34 to cancel any objectional ripple produced by the heater string 12.

Referring now to Fig. 3 there is shown a modification 70 of the full-wave doubler power supply of the present invention wherein any ripple produced at the heater output terminal 46, because of the heater current flowingthrough the capacitor 34} of the voltage doubler 28, is bucked out by a voltage derived at the heater output terminal 42 and applied to the capacitor 34 via a capacitor-resistance network 72. The network 72 comprises a pair of serially connected capacitors 74 and 76 connected in series with a pair of'serially connected resistors 78 and 86). One end of the resistor 80 and one end of the capacitor 74 are connected to the heater output terminal 42, and their other ends are connected to each other. The junction of the capacitor 76 andthe resistor 78 is connected to chassis ground, that is, to one end of the capacitor 34. The resistor 78 may be the resistance of a potentiometer Whose tap 82 is connected to the common junction of the resistance 78 and the capacitor 76. The purpose of this construction is to adjust the amplitude of the bucking voltage from the heater output terminal 4-2 to-the capacitor 34 and to compensate for the manufacturing tolerances of the capacitors 28, 3d, 3d, 7d and 76. In the embodiment '70 of the power supply, illustrated in Fig. 3, the low voltage end of the heater string 12 is connected to chassis ground through the relatively low D.-C. resistance of the choke 32;.

Thus, there has been shown and described herein the combination with a voltage doubler power supply of means for applying a safe operating voltage to a seriesconnected heater string. By connecting the series-connected heater, string to the A.-C. input terminals of the power supply through capacitive means, the D.-C. component of the voltage doubling circuit is isolated from the heater string, thereby preventing an excessive voltage between the heaters and their respective cathodes.

What is claimed. is:

l. in a power supply of the type wherein a pair of input terminals is connected to a voltage doubling circuit for rectifying and doubling an input A.-C. voltage, and having means for applying said rectified doubled voltage across a load, the combination therewith of means comprising a pair of heater output terminals for connecting aseries-connected heater string therebetween, means including a. capacitor to connect one of said pair of heater output terminals to one of said input terminals, and means connecting the other of said pair of heater output terminals to said voltage doubler circuit.

2. Apower supply comprising a pair of input terminals for applying a source of alternating current voltage there between, a first pair of output terminals for applying a load therebetween, a pair of diodes connected to each other inseries andhaving a common junction, means connecting one of said pair of input terminals to said common junction, a pair of serially connected capacitors having a common junction and connected in series with said diodes, means connecting the other of said pair of input terminals to said last-mentioned common junction, filter means connected between said pair of serially connected diodes, said first pair of output terminals being connected in series with said serially connected diodcs through said filter means, a second pair of output terminals for applying-a series-connected heater string therebetween, means including a capacitor to connect said one of said pair of input terminals to one of said second pair of output terminals, and meansconnecting the other of said second pair of output terminals with one of said serially connected capacitors.

3. In a power supply of the type wherein a pair of input terminals is connected to a voltage doubling circuit for rectifying and doubling an input A.-C. voltage, and having means for applying said rectified doubled voltage across a load, the combination therewith of means comprising a pair of heater output terminals for connecting a series-connected heater string therebetween, means including a first capacitor tocnnnect one of said pair of heater output terminals to one of said pair of input terminals, and means including a second capacitor connecting the other of said pair of heater output terminals to the other of said pair-of input terminals.

4-. In a power supply of the type wherein a pair of input terminals is connected to a voltage doubling circuit for rectifying and doubling an input A.-C. voltage, and

having means for applying said rectified doubled voltage between a first pair of output terminals, the combination therewith of means comprising a pair of heater output terminals for connecting a series-connected heater string therebetween, means including a capacitor to connect one of said pair of heater output terminals to one of said pair of input terminals, means including a portion of said voltage doubling circuit connecting the other of said pair of heater output terminals to the other of said pair of input terminals, and a capacitor connected between said one of said pair of heater output terminals and one of said first pair of output terminals.

5. In a power supply of the type wherein a pair of input terminals is connected to a voltage doubling circuit for rectifying and doubling an input A.-C. voltage, and having means for applying said rectified doubled voltage between a first pair of output terminals, the combination therewith of means comprising a pair of heater output terminals for connecting a series-connected heater string therebetween, means including a capacitor to connect one of said pair of heater output terminals to one of said pair of input terminals, said voltage doubling circuit comprising a pair of serially connected capacitors, means including one of said serially connected capacitors connecting the other of said pair of heater output terminals to the other of said pair of input terminals, and a resistancecapacitance network connecting said one of said pair of heater output terminals to one of said first pair of output terminals.

6. A power supply comprising a pair of input terminals for applying a source of alternating current voltage therebetween, a first pair of output terminals for applying a load therebetween, a pair of diodes connected to each other in series and having a common junction, means connecting one of said pair of input terminals to said common junction, a pair of serially connected capacitors having a common junction and connected in series with said diodes, means connecting the other of said pair of input terminals to said last-mentioned common junction, filter means connected between said pair of serially connected diodes, said first pair of output terminals being connected in series with said serially connected diodes through said filter means, a second pair of output terminals for applying a filament string therebetween, means including a first capacitor to connect said one of said pair of input terminals to one of said second pair of output terminals, and means including a second capacitor connecting the other of said second pair of output terminals wtih said other of said pair of input terminals.

7. A power supply comprising a pair of input terminals for applying a source of alternating current voltage therebetween, a first pair of output terminals for applying a load therebetween, a pair of diodes connected to each other in series and having a common junction, means connecting one of said pair of input terminals to said common junction, a pair of serially connected capacitors having a common junction and connected in series with said diodes, means connecting the other of said pair of input terminals to said last-mentioned common junction, filter means connected between said pair of serially connected diodes, said first pair of output terminals being connected in series with said serially connected diodes through said filter means, a second pair of output terminals for applying a filament string therebetween, means including a first capacitor to connect said one of said pair of input terminals to one of said second pair of output terminals, and means including one of said pair of serially connected capacitors connecting the other of said second pair of output terminals with said other of said pair of input terminals.

8. A power supply comprising a pair of input terminals for applying a source of alternating current voltage therebetween, a first pair of output terminals for applying a load therebetween, a pair of diodes connected to each other in series and having a common junction, means connecting one of said pair of input terminals to said common junction, a pair of serially connected capacitors having a common junction and connected in series with said diodes, means connecting the other of said pair of input terminals to said last-mentioned common junction, filter means connected between said pair of serially connected diodes, said first pair of output terminals being connected in series with said serially connected diodes through said filter means, a second pair of output terminals for applying a filament string therebetween, means including a capacitor to connect said one of said pair of input terminals to one of said second pair of output terminals, and means connecting the other of said second pair of output terminals in series with said pair of serially connected capacitors.

9. A power supply comprising a pair of input terminals for applying a source of alternating current voltage therebetween, a first pair of output terminals for applying a load therebetween, a pair of diodes connected to each other in series and having a common junction, means connecting one of said pair of input terminals to said common junction, a pair of serially connected capacitors having a common junction and connected in series with said diodes, means connecting the other of said pair of input terminals to said last-mentioned junction, filter means connected between said pair of serially connected diodes, said first pair of output terminals being connected in series with said serially connected diodes through said filter means, a second pair of output terminals for applying a filament string therebetween, means including a first capacitor to connect said one of said pair of input terminals to one of said second pair of output terminals, means connecting the other of said second pair of output terminals to said serially connected capacitors, and means including a second capacitor connecting said one of said second pair of output terminals to one of said first pair of output terminals.

No references cited. 

